Slim Zaidi

A Distributed Amplify-and-Forward Beamforming Technique in Wireless Sensor Networks

We consider L far-field terminals with one source and L-1 interferences that transmit to a wireless sensor network (WSN) with K uniformly distributed relaying nodes. Each relaying node receives a signal mixture from the L transmitters in the first phase, multiplies it with a properly selected beamforming weight and retransmits the resultant signal to a single receiving terminal in the second phase. The decentralized nature of the WSN dictates every node to compute its beamforming weight based only on its limited locally available information and without the knowledge of the locations and the channels of any other node in the network. Unfortunately, the optimal beamforming weights that maximize the signal-to-interference-plus-noise ratio (SINR) at the receiver cannot be computed locally. To circumvent this problem, we derive accurate local approximates of the SINR-optimal beamforming weights. Our proposed beamforming technique uses the so-obtained locally computable weights and, hence, can be implemented in a distributed fashion. The performance of the proposed distributed beamformer is analyzed both when the directions of the interferences are perfectly known and when they are imperfectly estimated. The advantages of the proposed distributed beamformer in comparison with a conventional distributed beamformer are analytically proved and are further verified by various simulation results.

Approximation algorithms for maximum link scheduling under SINR-Based interference model

An accurate localization algorithm tailored for anisotropic wireless sensors networks (WSNs) is proposed in this paper. Using the proposed algorithm, each regular or position-unaware node estimates its distances only to reliable anchors or position-aware nodes. The latter are properly chosen following a new reliable anchor selection strategy that ensures an accurate distance estimation making thereby our localization algorithm more precise. It is shown that the proposed algorithm is implementable in both 2-dimensional (2D) and 3-dimensional (3D) scenarios. A power saving mechanism aiming to enhance the WSN lifetime is also envisaged in this paper. It is proven that the proposed algorithm could easily incorporate such a mechanism. Simulations show that our algorithm, whether combined or not with the power saving mechanism, consistently outperforms the best representative localization algorithms currently available in the literature in terms of accuracy, even with the presence of nonuniform node distribution or radiation irregularities.

Efficient range-free localization algorithm for randomly distributed wireless sensor networks

In this paper, we propose a novel range-free localization algorithm able to reduce errors due to mapping the hops into distance units. Using the proposed algorithm, the mean hop size h̅s is locally derived at each regular or position-unaware node, thereby avoiding its broadcast by anchors (i.e., a few nodes aware of their exact position) as usually required in current state-of-the-art solutions and, hence, resulting in less battery power depletion. The analytical expression of h̅s is derived for different node distributions. Furthermore, it is shown that it is possible to locally compute h̅s at each regular node with or even without prior knowledge of the node distribution. Simulations results show that the proposed scheme outperforms the most representative range-free localization schemes in terms of accuracy.

Range-free localization algorithm for heterogeneous Wireless Sensor Networks

In this paper, we propose a novel range-free localization algorithm tailored for heterogeneous wireless sensor networks (WSNs), where nodes have different transmission capabilities. Two different approaches are developed to accurately derive the expected hop progress (EHP). It is shown that the obtained EHP depends solely on the information locally available at each node and, hence, can be computed in a localized manner. Furthermore, a localization correction mechanism which accounts for the heterogeneous nature of WSNs is developed. Simulations results show that the proposed algorithm, whether with or without correction, outperforms in accuracy the most representative range-free localization algorithms in the literature.

Distributed Collaborative Beamforming in the Presence of Angular Scattering

In this paper, a collaborative beamformer (CB) is considered to achieve a dual-hop communication from a source to a receiver, through a wireless network comprised of K independent terminals. Whereas previous works neglect the scattering effect to assume a plane-wave single-ray propagation channel termed here as monochromatic (with reference to its angular distribution), a multi-ray channel termed as polychromatic due to the presence of scattering is considered, thereby broadening the range of applications in real-world environments. Taking into account the scattering effects, the weights of the so-called polychromatic CB (P-CB) are designed so as to minimize the received noise power while maintaining the desired power equal to unity. Unfortunately, their derivation in closed-form is analytically intractable due to the complex nature of polychromatic channels. However, when the angular spread (AS) is relatively small to moderate, it is proven that a polychromatic channel may be properly approximated by two rays and hence considered as bichromatic. Exploiting this fact, we introduce a new bichromatic CB (B-CB) whose weights can be derived in closed-form and, further, accurately approximate the P-CBs weights. Yet these weights, which turn out to be locally uncomputable at every terminal, are unsuitable for a distributed implementation. In order to circumvent this shortcoming, we exploit the asymptotic expression at large K of the B-CB whose weights could be locally computed at every terminal and, further, well-approximate their original counterparts. The performances of the so-obtained bichromatic distributed CB (B-DCB) and its advantages against the monochromatic DCB (M-DCB), which is designed without accounting for scattering, are analytically proved and further verified by simulations at practical values of K.

Range-Free Localization Algorithm for Anisotropic Wireless Sensor Networks

In this paper, we propose a novel range-free localization algorithm tailored for anisotropic wireless sensors networks (WSN)s. Using the proposed algorithm, each regular or positionunaware node estimates its distances only to reliable anchors or position-aware nodes. The latter are properly chosen following a new reliable anchor selection strategy that ensures an accurate distance estimation making thereby our localization algorithm more precise. Indeed, simulations suggest that it outperforms the best representative range- free localization algorithms currently available in the literature in terms of accuracy.

SNR and throughput analysis of distributed collaborative beamforming in locally-scattered environments

Three main collaborative beamforming (CB) solutions based on different channel models exist: the optimal CSI-based CB (OCB), the conventional or monochromatic (i.e., single-ray) distributed CB (M-DCB), and the recently developed bichromatic (i.e., two-ray) distributed CB (B-DCB). In this paper, we perform an analytical comparison, under practical constraints, between these CB solutions in terms of achieved signal-to-noise ratio (SNR) as well as achieved throughput. Assuming the presence of local scattering in the source vicinity and accounting for implementation errors incurred by each CB solution, we derive for the first time closed-form expressions of their true achieved SNRs. For low angular spread (AS), where both solutions nominally achieve the same SNR in ideal conditions, we show that the B-DCB always outperforms OCB, more so and at larger regions of AS values when errors increase. Excluding exceptional circumstances of unrealistic low quantization levels (i.e., very large quantization errors) that are hard to justify in practice, we also show that the new B-DCB always outperforms the M-DCB as recently found nominally in ideal conditions. This work is also the first to push the performance analysis of CB to the throughput level by taking into account the feedback overhead cost incurred by each solution. We prove both by concordant analysis and simulations that the B-DCB is able to outperform, even for high AS values, the OCB which is penalized by its prohibitive implementation overhead, especially for a large number of collaborating terminals and/or high Doppler frequencies. Indeed, it is shown that the operational regions in terms of AS values over which the new B-DCB is favored against OCB in terms of achieved throughput can reach up to 40°. Copyright

Analysis of collaborative beamforming designs in real-world environments

Three main collaborative beamforming (CB) designs based on different channel models could be applied in real-world environments where local scattering and implementation imperfections might exist: the optimal CSI-based CB (OCB), the conventional or monochromatic (i.e., single-ray) distributed CB (M-DCB), and the recently developed bichromatic (i.e., two-ray) distributed CB (B-DCB). In this paper, we perform an analytical comparison, under practical constraints, between these CB designs in terms of achieved signal-to-noise ratio (SNR) as well as achieved throughput. Assuming the presence of local scattering in the source vicinity and accounting for implementation errors incurred by each CB design, we derive for the first time closed-form expressions of their true achieved SNRs. At a low angular spread (AS) where both designs nominally achieve the same SNR in ideal conditions, we show that the B-DCB always outperforms OCB, more so and at larger regions of AS values when errors increase. Excluding exceptional circumstances of unrealistic low quantization levels (i.e., very large quantization errors) hard to justify in practice, we also show that the new B-DCB always outperforms the M-DCB as recently found nominally in ideal conditions. This work is also the first to push the performance analysis of CB to the throughput level by taking into account the feedback overhead cost incurred by each design. We prove both by concordant analysis and simulations that the B-DCB is able to outperform, even for high AS values, the OCB which is penalized by its prohibitive implementation overhead, especially for a large number of collaborating terminals and/or high Doppler frequencies.

Distributed Beamforming for Wireless Sensor Networks in Local Scattering Environments

In this paper, transmit and receive collaborative beamforming (CB) techniques are considered to achieve a dualhop communication from a source to a receiver, through a wireless sensor network (WSN). Whereas the previous works assumed a model of plane wavefronts, here, a local scattering in the source or receiver vicinity is considered, thereby broadening the range of applications in real-world environments. Taking into account the local scattering, these beamformers aim to maintain the beamforming response in the desired direction equal to unity. It is shown that the so-obtained beamformers are not suitable for a distributed implementation in WSNs. We hence propose a novel distributed collaborative beamforming (DCB)technique that can be implemented in a distributed fashion and, further, well-approximates both transmit and receive CB techniques. The performance of the proposed DCB is analyzed and its advantages against the conventional DCB, which is designed without taking into account the presence of local scattering in the source or receiver vicinity, are analytically proved and are further verified by simulations.

Distributed collaborative beamforming with minimum overhead for local scattering environments

In this paper, transmit and receive collaborative beamforming (CB) techniques are considered to achieve a dualhop communication from a source to a receiver, through a wireless network comprised of K independent terminals. Whereas the previous works assumed a model of plane wavefronts, here, a local scattering in the source or receiver vicinity is considered, thereby broadening the range of applications in real-world environments. Taking into account the local scattering, these CB techniques aim to maintain the beamforming response in the desired direction equal to unity. It is shown that the so-obtained collaborative beamformers are not suitable for a distributed implementation. We hence propose a novel beamformer solution that can be implemented in a distributed fashion and, further, well-approximates both transmit and receive collaborative beam-formers. The performance of the proposed distributed CB (DCB) technique is analyzed and its advantages against the conventional DCB technique, which is designed without taking into account the presence of local scattering in the source or receiver vicinity, are analytically proved and further verified by simulations.